Kittisakmontri, Kulnipa; (2022) The impact of dietary protein in complementary foods on infant growth and iron status in a population facing double burden of malnutrition. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

Dietary protein is a key macronutrient for infant growth, especially during complementary feeding (CF). Inadequate intake contributes to undernutrition. However, evidence from high-income countries suggests high protein intake, especially of animal-based protein (ABP), may increase obesity risk. Determining optimal protein intake and sources during CF is thus challenging, particularly in lower-income settings where the double burden malnutrition (DBM; co-existence of under- and overnutrition) is common; and considering that animal-source foods are a good source of iron during this period of high requirements. This thesis aimed to investigate how protein quantity and source during CF influence infant growth and iron status in a setting experiencing the DBM, and to explore potential mechanisms. A multi-centre, prospective cohort was conducted in 145 healthy-term infants in Chiang Mai, Thailand. Dietary intakes and anthropometric measurements were collected at 6, 9 and 12M. At 12M, blood samples were analysed for iron status, serum IGF-1, IGFBP-3 and plasma branched-chain amino acids (BCAA). Protein consumption exceeded recommendations at 9-12M. Both dairy and non-dairy ABP were positively associated with weight-for-age and weight-for-length z-scores after adjusting for type of milk-feed and non-protein calories, with no effect on linear growth. Dairy ABP showed a stronger association than non-dairy ABP, consistent with its higher association with IGF-1, IGFBP-3 and BCAA. Protein intake did not differ significantly between iron-sufficient versus iron-deficient (ID) infants, but consumption of ≥ 3 tablespoons of liver/week was associated with a nearly 80% reduction in ID. The findings highlight differential effects of protein source on infant growth and iron status. Unlike dairy protein, non-diary ABP may promote growth without greatly increasing IGF-1, IGFBP-3 and BCAA which are implicated in increased obesity risk whilst also representing a good source of iron. The findings could help develop interventions for testing in randomised trials to establish causal relationships and mechanisms and contribute to improving CF protein recommendations.

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